Iarnród Éireann yesterday confirmed plans to spend millions of euro on Dublin's little-known Phoenix Park tunnel to provide a rail link for commuters travelling to the city centre and the International Financial Services Centre (IFSC) in North Wall.

The €13.5 million renovation of the 692-metre underground railway line, which will also include a new signalling works at Connolly, will allow train users to avail of new direct services to Connolly, Tara Street, Pearse Street and Grand Canal Dock stations from autumn 2016.

However, an Iarnród Éireann spokesman last night told The Irish News that the project would have “no effect” on people travelling from Northern Ireland to cities beyond Dublin.

The north's rail users will be able to catch a connection from Connolly to Kildare from next year, but if they want to head to Cork, Limerick, Galway or elsewhere they will still have to use a Luas tram or hop on a bus to Heuston station three-miles away on the other side of the Liffey River.

The spokesman said a third option might become available if funding for a €4 billion DART Underground service gets the go-ahead next month. However, a final decision has not yet been made, and any potential new service would not become operational until the distant future.

“For the moment, it's going to have to be the Luas,” he added.

Mark Gleeson of Rail Users Ireland, a group set up in 2013 to represent the Republic's rail travellers, complained that the current arrangements for those travelling between Belfast and Cork were inconvenient and costly.

Mr Gleeson suggested that Iarnród Éireann and Translink should work together to find a way to make the journey more cost-effective and easier for those travelling beyond Dublin, but he admitted that tight budgets would be a key factor in any future decisions.

He revealed that a direct service did run between the two cities in the 1950s but was “suspended for lack of use” while the north's Special Olympics team were allowed to use the Phoenix Tunnel to travel direct to Limerick last year.

A spokesman for Special Olympics Ulster confirmed that Translink staff had arranged with their southern counterparts in both 2010 and 2014 for a train carrying hundreds of athletes to use the tunnel, avoiding the hassle of making their way across the city.

“We were very grateful. We couldn't have managed without it,” the sporting body's spokesman said.

In the past, rail chiefs have also allowed the tunnel to be used by fans travelling to Croke Park to attend All-Ireland finals or to go to big-name concerts. However, the rail line is most often used for freight.

Announcing news of the planned upgrade yesterday, the Republic's transport minister Paschal Donohoe said: “For the first time, commuters on the popular Kildare suburban rail line will have frequent services directly into the heart of the south city business district.

“This will provide an attractive alternative for private motorists who currently commute into the city along the congested N7 corridor.”

Iarnród Éireann chief executive David Franks, said the works would mean improved connections for new and existing commuters, adding: “They will be of particular benefit for those commuting between the Kildare line and the south city area served by Pearse and Grand Canal Dock, offering direct connections which are not currently available by public transport.”

The Phoenix Tunnel was completed in 1877 by the Great Southern and Western railway company.